The power source apparatus is provided with a plurality of modules (10), and a main controller (2) connected with communication interface units (16) in each module via a communication line CB. Each module is provided with a battery block (12) having a plurality of battery cells (11) stacked together and connected in series and/or parallel, a battery state detection section (14) to detect the state of the battery cells, communication interface units for data communication with other modules and the main controller, and a memory section (18) that can store data received through the communication interface units. The plurality of modules are connected in series and/or parallel with an output line OL.